ScriptCraft/scriptcraft/src/main/java/com/thebrokenrail/scriptcraft/core/quickjs/QuickJSManager.java

package com.thebrokenrail.scriptcraft.core.quickjs;

import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;

public class QuickJSManager {
    private static QuickJSNative quickjs;

    public static abstract class Task {
        private boolean lastTask = false;
        private boolean done = false;
        private boolean err;
        private Object obj;

        protected abstract Object run(QuickJSNative quickjs) throws JSException;
    }

    private static Thread thread;

    private static final AtomicReference<Task> quickJSInputTask = new AtomicReference<>();

    private static final AtomicReference<Task> quickJSOutputTask = new AtomicReference<>();

    public static Object sendTaskFromQuickJS(Task task) {
        if (Thread.currentThread() != thread) {
            throw new RuntimeException();
        }
        task.done = false;
        task.err = false;
        synchronized (lock) {
            quickJSOutputTask.set(task);
            lock.notifyAll();
            while (!task.done) {
                try {
                    lock.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
        if (task.err) {
            throw new RuntimeException("Java Exception While Executing Task: " + task.obj);
        } else {
            return task.obj;
        }
    }

    private static final Object startedLock = new Object();

    private static class QuickJSThread extends Thread {
        private QuickJSThread() {
            super("QuickJS thread");
        }

        @Override
        public void run() {
            synchronized (lock) {
                init();

                while (true) {
                    try {
                        lock.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    Task task = quickJSInputTask.get();
                    if (task != null && !task.done) {
                        try {
                            task.obj = task.run(quickjs);
                        } catch (Throwable e) {
                            e.printStackTrace();
                            task.obj = null;
                        }
                        task.done = true;
                        if (task.lastTask) {
                            break;
                        }
                    }
                    lock.notifyAll();
                }
            }
        }

        private void init() {
            try {
                quickjs = new QuickJSNative();
                synchronized (startedLock) {
                    startedLock.notifyAll();
                }
            } catch (JSException e) {
                started.set(false);
                synchronized (startedLock) {
                    startedLock.notifyAll();
                }
                throw new RuntimeException(e);
            }
        }
    }

    private static final AtomicBoolean started = new AtomicBoolean(false);

    public static void init(Task initTask) {
        if (!started.get()) {
            started.set(true);

            thread = new QuickJSThread();

            synchronized (startedLock) {
                thread.start();
                try {
                    startedLock.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

            if (!started.get()) {
                return;
            }

            sendTaskToQuickJS(initTask);

            Runtime.getRuntime().addShutdownHook(new Thread(() -> {
                started.set(false);
                Task task = new Task() {
                    @Override
                    protected Object run(QuickJSNative quickjs) {
                        System.out.println("Freeing QuickJS");
                        quickjs.free();
                        return null;
                    }
                };
                task.lastTask = true;
                sendTaskToQuickJS(task);
            }));
        }
    }

    private static final AtomicBoolean lock = new AtomicBoolean(false);

    public static synchronized Object sendTaskToQuickJS(Task task) {
        if (!started.get()) {
            return null;
        }
        synchronized (lock) {
            if (lock.get()) {
                throw new RuntimeException();
            } else {
                lock.set(true);
                quickJSOutputTask.set(null);
                quickJSInputTask.set(task);
                lock.notifyAll();
                if (task.lastTask) {
                    return null;
                } else {
                    do {
                        try {
                            lock.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        Task outputTask = quickJSOutputTask.get();
                        if (outputTask != null && !outputTask.done) {
                            try {
                                outputTask.obj = outputTask.run(null);
                                outputTask.err = false;
                            } catch (Throwable e) {
                                StringWriter writer = new StringWriter();
                                e.printStackTrace(new PrintWriter(writer));
                                outputTask.obj = writer.toString();
                                outputTask.err = true;
                            }
                            outputTask.done = true;
                            quickJSOutputTask.set(outputTask);
                        }
                        lock.notifyAll();
                    } while (!task.done);
                }
                lock.set(false);
                return task.obj;
            }
        }
    }
}